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1. Field of the Invention
The present invention relates to a proportioner for proportioning a fluid flow, when medicaments are to be dosed in the field of medical engineering.
2. Description of Prior Art induding information disclosed under 37 CFR 1.97 and 1.98
In the field of medical engineering, proportioners are known, which comprise flow resistors whose flow rate depends on the pressure with which the medium to be proportioned is acted upon before the flow resistor, when seen in the direction of flow. For detecting the pressure difference, two different pressure sensors are normally used, the pressure sensors being arranged before and after the flow resistor, when seen in the direction of flow.
Known flow resistors consist e.g. of glass capillaries or microchannels in a capillary form. A disadvantage of such known proportioners is that they have a complicated structural design due to the fact that a flow resistor and two different pressure sensors, which arranged before and after the flow resistor when seen in the direction of flow, are required.
In the Patent Abstracts of Japan, P 1828, Nov. 18, 1994, Vol. 18, No. 609, a means for measuring a flow rate is described, in the case of which an elastic plate with an opening is arranged in a passage or in a tube through which fluid flows. Furthermore, means for detecting the deflection of the elastic plate are provided in the elastic plate.
DE 195 29 396 A1 discloses a measuring device for measuring the flow rate of a medium flowing in a flow cross-section, in the case of which a plate acted upon by the medium is flexible due to cuts formed therein, the plate having provided thereon strain gauges for detecting a deflection of the plate.
DE 42 23 067 C2 describes a micromechanical flow restrictor which is implemented in a multilayer structure. This flow restrictor is adapted to be used in combination with a micromechanical valve for micromechanical proportioners.
DE 19 43 021 AS teaches that a means is used for measuring the flow through a tube according to the differential pressure flow metering method in the case of which an elastic deformation of a component depending on the pressure to be measured is converted into an electric signal. The strain gauges used for detecting the elastic deformation are directly attached to an elastic orifice plate which is arranged in the tube through which the fluid flows.
It is the object of the present invention to provide a proportioner with a simple structural design, which permits exact proportioning of a medium to be proportioned and which also offers the possibility of detecting clogging of the proportioner.
In accordance with a first aspect of the invention, this object is achieved by a proportioner for proportioning a fluid flow from an input side of a first proportioning element to an output side of a second proportioning element, said first and second proportioning elements comprising a membrane provided with at least one opening acting as a flow resistor for a medium to be proportioned, and a pressure sensor integrated in the membrane and used for detecting a pressure difference between the input side and the output side of the proportioning element. The proportioner comprises a pressure transducer for input-side application of a pressure to the medium to be proportioned. The first and the second proportioning element are arranged in succession so as to permit, on the basis of the pressure drop across the membranes of the two proportioning elements, the detection of clogging or blocking of the respective flow resistor provided in said membranes.
In accordance with a second aspect, the present invention provides a proportioner for proportioning a fluid flow from an input side of a proportioning element to an output side thereof, the propotioning element comprising a membrane provided with at least one opening acting as a flow resistor for a medium to be proportioned and a pressure sensor integrated in the membrane and used for detecting a pressure difference between the input side and the output side of the proportioning element. A passive flow resistor is arranged before or after the proportioning element when seen in the direction of flow, wherein the proportioner comprises a when seen in the direction of flow, wherein the proportioner comprises a pressure transducer for input-side application of a pressure to the medium to be proportioned, and wherein detection of clogging or blocking of the flow resistor provided in the membrane is possible on the basis of the pressure drop across the membrane of the proportioning element.
The proportioning elements preferably consists of a semiconductor chip provided with a semiconductor membrane, the pressure sensor being defined by piezoresistive resistors arranged on or in the membrane. In addition, the semiconductor chip, which can consist e.g. of silicon, has preferably integrated therein a temperature sensor.
Preferably, a control device is provided for controlling the controllable pressure transducer in dependence upon the pressure difference detected by means of the pressure sensor and/or the temperature detected by means of the temperature sensor.
An alarm signalling device can be provided for outputting an alarm if flow passages arranged before and/or after the membrane have a leak or are clogged or if the at least one opening of the membrane is clogged; such malfunctions can be recognized on the basis of the pressure difference detected by the pressure sensor.
In comparison with known proportioners, the proportioner according to the present invention is advantageous insofar as the pressure difference is determined directly by means of a sensor instead of being determined by two pressure measurements relative to the atmosphere, the results of the two measurements being then subtracted from one another. Furthermore, the flow resistor, i.e. the restriction, according to the present invention is integrated directly in the pressure sensor. Hence, only a single chip is required, the chip fulfilling both the function of differential pressure measurement and the function of the flow resistor, i.e. the flow restricting function.
Further developments of the present invention are disclosed in the dependent claims.